This invention relates to towed marine sensors used in seismic exploration and more particularly to an improved hydrophone line array.
In the practice of marine seismic sensings, a surface ship tows a 50 to 2,000 meter length of sensor line through the water in a submerged generally horizontal position. One form of such prior art sensor line is a series of longitudinally spaced transducers, such as piezoelectric crystals, mechanically integrated in a unitary body and connected by individual leads to signal processing and recording apparatus on the towing ship. The transducers in such line respond to reflections of acoustic wave energy from the floor of the sea and provide the desired data for identifying geological characteristics essential to a determination of the oil and mineral content of the explored regions. A typical hydrophone array using piezoelectric crystal transducers is described in U.S. Pat. No. 3,739,376.
Piezoelectric and similar transducers are delicate devices and their use in marine sensor lines has required considerable care to prevent damage to them. The repeated winding and unwinding of the line on and from the storage reel continually exposes the fragile transducer elements to impacts and stresses which adversely affect their sensitivity and life. As a consequence, such transducers are mounted within the line structure so as to protect them against such damage while at the same time attempting to maintain maximum exposure and sensitivity to acoustical wave energy incident to underwater exploration. One prior art technique for doing this is to immerse the transducers in long oil-filled plastic tubes. Such an array is heavy and bulky to tow, difficult to store and costly to construct and maintain.
Another disadvantage of prior art hydrophones is that the piezoelectric or similar transducer elements provide point omnidirectional sensitivity at spaced intervals along the array. This limits the resolution capability of the line which may be partially compensated by increasing the number of transducer elements at a corresponding increase in cost of the array.